A so-called cordless electric tool using a charging-type battery pack as an electric-power source is widely spread. The battery pack normally incorporates a cell set, which is formed by serially connecting a plurality of battery cells, and lithium ion batteries are a mainstream as a battery type. The battery pack using the lithium ion batteries incorporates a protecting IC for monitoring the voltages of the respective battery cells or a voltage monitoring means having a function equivalent to that (protecting IC). If any of the battery cells is short-circuited or the voltage of the battery cell has reached a threshold of reaching an overdischarge state, an alarm signal is output from the protecting IC, and this is for stopping usage of the battery pack in response to that.
An electric tool which sets usage of the battery pack incorporating the protecting IC as a condition is configured to turn off a switching element, which is formed by a FET or the like provided on a current path flowing from the battery pack to a motor in the electric tool, in response to the alarm signal output from the protecting IC and forcibly terminate usage of the battery pack (for example, see Patent Document 1).